Say “skeleton” to children and you probably conjure up in their minds a rickety structure of rigid sticks, or, to the more fanciful child, a clickety-clacketing collection of rattling bones cavorting under a Halloween moon. A look at almost any anatomical drawing of the human skeletal system bears out the child's image: dry sticks of bones, stripped of skin and flesh, muscle and tendon—a grotesque caricature of a living human being.

Most of us have heard often enough that the brain, acting as control center for a communication network we call our nervous system, is an incredible computer, weighing a mere three pounds. Its form and functions, however, are often described as being so much more intricate and complex than any existing or imagined computer that thorough knowledge of the brain seems very remote.

A physician once remarked that a great many people seem to spend about half their time getting food into their digestive tracts and the other half worrying about how that food is doing on its travels. The physician was exaggerating, but he made his point.

In large part our good health depends on the quality of the body's internal environment. There is a kind of ecological principle at work within us—if one chain threatens to break, one system becomes polluted, one balance is tilted, then the whole environment is in imminent danger of collapsing.